1. Field of the Invention
This invention relates broadly to turbine engines, and more particularly, to starters for turbine engines.
2. State of the Art
In a turbine jet engine, air is taken in from the outside, compressed, heated by the combustion of fuel, and then expanded in a turbine. The air is expelled from the engine through an exhaust pipe at a much higher velocity than the intake velocity, thereby creating a propulsive force. A turbine jet engine generally includes a compressor which draws air into the engine and compresses it into a combustion chamber. Vaporized (or atomized) liquid fuel, e.g., diesel or Jet A kerosene, is injected into the combustion chamber and heated to cause a self-sustaining burn. The burn causes a rise in temperature in the combustion chamber which increases the pressure of the air in the combustion chamber, which is then expanded through a turbine and expelled through the exhaust pipe at the rear of the engine. The turbine absorbs the necessary energy from the expanded high velocity air to power the compressor, with the greater part of the energy utilized to develop propulsive thrust.
Turbine engines, especially relatively small engines, can be difficult to start. One reason for this is that the dwell time of the fuel/air mixture in the combustion chamber is extremely short. As a consequence, there is little time to heat the liquid fuel to a temperature hot enough to self-sustain a flame.
It is therefore an object of the invention to provide a system for sustaining the combustion of a liquid fuel injected into a turbine engine upon starting the turbine engine.
It is another object of the invention to provide a system which rapidly increases the temperature of a combustion chamber of the turbine engine to a temperature high enough to allow the liquid fuel to be consumed in a self-sustaining manner.
In accord with these objects, which will be discussed in detail below, a turbojet engine is provided which includes a housing having a forward inlet nozzle, an aft exhaust pipe, and a combustion chamber therebetween. The aft exhaust pipe preferably includes a variable area nozzle to optimize engine performance. The engine also includes a compressor between the inlet nozzle and the combustion chamber, and a turbine between the combustion chamber and the exhaust pipe. A shaft couples the compressor and the turbine together such that rotation of the turbine cause rotation of the compressor. A liquid fuel injector and atomizer (or vaporizer) is provided to inject atomized (or vaporized) fuel into the chamber for combustion therein. In addition, a solid fuel element and a heater element to ignite the solid fuel is provided in the chamber.
When the engine begins a starting sequence, a starter begins spinning the compressor and an air flow is pumped through the engine. The solid fuel element is then heated by the heater element until the solid fuel begins to burn. The combustion of the solid fuel increases the temperature of the combustion chamber so that when, thereafter, a liquid fuel is injected and atomized, the temperature within the combustion chamber is sufficient to allow the liquid fuel to burn in a self-sustaining manner.